Antiferromagnetic coupling by spin polarized tunneling

By performing magnetic studies on Fe/MgO/Fe magnetic tunnel junctions, we provide experimental evidence of room-temperature antiferromagnetic coupling between two ferromagnetic layers across a very thin insulating barrier. Epitaxial growth of the MgO barrier on a very flat Fe layer leads to an extremely low "orange peel" magnetic coupling. Then, antiferromagnetic coupling is observed for MgO thickness, t(MgO), below 0.8 nm. The strength of this coupling increases abruptly when reducing t(MgO) down to 0.5 nm. The shape of the variation of experimental coupling strength J with t(MgO), the quantitative value of \J\, and finally, the thickness range of t(MgO) for which the antiferromagnetic coupling is observed are in good agreement with the equilibrium interlayer exchange theory by the spin polarized quantum tunneling of electrons between the ferromagnetic layers. (C) 2003 American Institute of Physics.